Maraging steel is a term of the art derived from "martensite age hardening", These alloys are currently the iron- nickel-cobalt-molybdenum alloys as described in the cobalt monograph series entiltled "Cobalt-containing high strenth steels", Centre D'Information Du Cobalt, Brussels, 1974, pp. 50-51. Readily oxidizable metals such as Al, V and/or Ti at low levels e.g. 1% by weight or below can be added.
Metal alloy powders heretofore have been produced by gas or water atomization of molten ingots of the alloy. It has not been generally practical to produce the metal alloy powders directly from the individual metal powders because of the difficulty in obtaining uniformity of distribution of the metals. It is difficult to obtain certain powders containing readily oxidizable metals such as aluminum because of the tendency of those metals to form the respective oxides during processing.
U.S. Pat. No. 3,663,667 discloses a process for producing multimetal alloy powders. Thus, multimetal alloy powders are produced by a process wherein an aqueous solution of at least two thermally reducible metallic compounds and water is formed, the solution is atomized into droplets having a droplet size below about 150 microns in a chamber that contains a heated gas whereby discrete solid particles are formed and the particles are thereafter heated in a reducing atmosphere and at temperatures from those sufficient to reduce said metallic compounds to temperatures below the melting point of any of the metals in said alloy.
U.S. Pat. No. 3,909,241 relates to free flowing powders which are produced by feeding agglomerates through a high temperature plasma reactor to cause at least partial melting of the particles and collecting the particles in a cooling chamber containing a protective gaseous atmosphere where the particles are solidified. In this patent the powders are used for plasma coating and the agglomerated raw materials are produced from slurries of metal powders and binders. Both the 3,663,667 and the 3,909,241 patents are assigned to the same assignee as the present invention.
In European Patent Application W08402864 published Aug. 2, 1984, also assigned to the assignee of this invention, there is disclosed a process for making ultra-fine powder by directing a stream of molten droplets at a repellent surface whereby the droplets are broken up and repelled and thereafter solidified as described therein. While there is a tendency for spherical particles to be formed after rebounding, it is stated that the molten portion may form elliptical shaped or elongated particles with rounded ends.
It is believed therefore that a relatively simple process which enables finely divided maraging steel alloy powders containing at least one readily oxidizable metal having a spherical particle shape to be produced from sources of the individual metals by agglomerating and utilizing high temperature melting is an advancement in the art.